Octopuses are social animals that change colours to resolve disputes and even throw debris at each other, video footage of a group of the feisty sea creatures in Jervis Bay has shown.

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Key points:

Octopuses thought to be solitary animals, but video of rare group shows they have dramatic social lives

Octopuses signal to each other using colour to indicate their mood

Researchers binge-watched 52 hours of video to see how octopuses interacted

The octopuses' unusual behaviour was first observed by a local diver — study co-author Matthew Lawrence — who mentioned their social gathering on a cephalopod enthusiast website.

It immediately attracted the attention of an international team of octopus experts, including Professor Peter Godfrey-Smith from the University of Sydney and City University of New York and Professor David Scheel from Alaska Pacific University.

They set up underwater cameras to film the octopuses interacting.

The study, published today in Current Biology, documents a very rare example of octopuses living in a group.

Octopuses have generally been viewed as solitary creatures, and their colour-changing abilities primarily as a means to hide from hungry predators.

But after binge-watching hours of footage, the researchers discovered not only did the octopuses live together, they also used their colour-changing abilities, along with extreme body postures, to avoid conflict in social interactions with other octopuses.

Living in groups is rare

Up to a dozen Sydney octopuses (Octopus tetricus) inhabit a three-metre-square area in the middle of Jervis Bay, with the site centring on an encrusted object in the midst of a sandy expanse.

"Octopus began living there and dropped the shells of the scallops they had eaten. Over time the shell midden built up, providing good building materials for new arrivals to create dens," Professor Godfrey-Smith said.

But the octopuses were not hanging about because they liked each other or wanted to be in close proximity, he said.

"There are scallops everywhere, providing an almost unlimited food source, while the mound of scallop shells provides an island of safety amidst a sea of predators including sharks, dolphins, seals and pack-hunting leatherjackets," Professor Godfrey-Smith said.

"Perhaps they are just tolerating each other; perhaps there's more engagement. [We know] they mate at the site as well."

During the 52 hours of footage collected, the octopuses interacted with each other 186 times, and engaged in a range of actions, from standing tall, to raising their mantle over their head, throwing debris at or poking each other, spreading their webs, or darkening their skin tone.

"When one octopus sees another dark-skinned octopus approaching, it may 'go dark', indicating that the encounter is likely to escalate," Professor Godfrey-Smith said.

Like other cephalopods, octopuses are able to change colour and pattern by dilating or contracting chromatophores in their skin.

"They then stand tall with their web spread in what we call the Nosferatu pose, after the classic film vampire, with the encounter likely leading grappling or other acts of aggression," Professor Godfrey-Smith said.

When a dark octopus approaches a pale one, however, the pale animal usually retreats, while a dark octopus approached by one with more subdued colours is more likely to stand its ground.

"We don't know exactly why they engage in these heated exchanges. It could be an attempt by one or more animals to control territory, as we saw males excluding males but not females, but this isn't always the case," Professor Godfrey-Smith said.

Watching octopus TV is 'harder than it sounds'

Professor Godfrey-Smith and Professor Scheel enlisted the help of a group of students to analyse the video.

"They binge-watched 52 hours of GoPro footage of octopuses walking around and poking each other, scoring the octopuses' moods by measuring their pixels of their skin colour against those in the background," Professor Godfrey-Smith said.

"It's harder than it sounds. Trying to keep track of who's who is very difficult. They can change colour or shape in a second, and when one moves into view it is hard to tell whether they are a new animal -- or one that you've been watching for ages.

"We would love to know to what extent this behaviour was about males trying to control territory or whether it was part of a richer and more complicated social life that we are only just becoming aware of."

Octopus in foreground turn pales when retreating from confrontation with another octopus in the background.

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